Hydrorefining is a well-known process for upgrading a variety of hydrocarbon fractions. The term "hydrorefining" is used herein to designate a catalytic treatment in the presence of hydrogen of a hydrocarbonaceous oil in order to upgrade the oil by eliminating or reducing the concentration of contaminants in the oil such as sulfur compounds, nitrogenous compounds, metal contaminants and/or partial saturation of the oil.
U.S. Pat. Nos. 3,953,321 and 4,098,721 disclose a hydrodesulfurization process for heavy hydrocarbonaceous oils such as gas oils in which a conventional hydrodesulfurization catalyst is sulfided and heat treated at a temperature of 750.degree. F. to 850.degree. F. prior to initiating the hydrodesulfurization. The catalyst is sulfided by contact with a lighter boiling range oil or is heat treated in the presence of the lighter oil, free from sulfur.
U.S. Pat. No. 2,954,339 discloses the use of a spent cobalt-molybdenum-alumina catalyst for hydrodesulfurization of a hydrocarbonaceous oil which may be a gas oil. Prior to contact with the gas oil, the catalyst is used to hydrotreat naphtha.
U.S. Pat. No. 3,423,307 discloses a start-up method for a hydrodesulfurization process for heavy residual feeds which contain asphaltic materials. The catalyst is initially contacted with an asphaltic-free feed.
U.S. Pat. No. 3,528,910 discloses a hydrotreating process for hydrocarbonaceous oils. A catalyst, such as a supported nickel-molybdenum catalyst, is sulfided in the presences of hydrogen with a distillate containing disulfide sulfur prior to the hydrotreating reaction.
U.S. Pat. No 4,149,965 discloses a start-up process for hydrorefining of naphtha. The catalyst is partially deactivated by treatment with a substantially non-metal containing hydrocarbon oil in the presence hydrogen prior to contacting the catalyst with the naphtha feed.
U.S. Pat. No. 3,368,965 discloses a slurry hydrogenation process in which a catalyst, such as cobalt molybdate on alumina, is pretreated by wetting the catalyst with a clean (i.e., non-aromatic) hydrocarbonaceous oil such as a lubrication oil fraction to form a slurry which is then introduced into the hydrocarbonaceous oil to be hydrogenated.
U.S. Pat. No. 3,423,307 utilizes a start-up method comprising initially contacting a hydrorefining catalyst with hydrogen and an asphaltic-free hydrocarbon at a temperature from 250.degree. F. to 500.degree. F. and then gradually increasing the temperature until a temperature within the range of 600.degree. F. and 700.degree. F. is attained, following which hydrorefining of an asphaltic-containing feed is commenced.
U.S. Pat. No. 4,485,006 initiates the hydrorefining process by initially contacting a sulfided hydrorefining catalyst, such as nickel-molybdenum on alumina, with a light hydrocarbonaceous oil boiling in the range of C.sub.5 to 700.degree. F., in the presence of hydrogen, and thereafter contacting the catalyst with the heavy hydrocarbonaceous oil to be hydrorefined.
It has now been found that by utilizing the particular slow start-up rate of the instant invention, enhanced catalyst activity can be obtained without the need for initially contacting the catalyst with an oil that is lighter than the feed oil.